1. Field of the Invention
This invention relates to ridge waveguide filters and more particularly to evanescent mode ridge waveguide filters embedded in multilayer ceramic structures.
2. Description of Related Art
Waveguide filters embedded in Low Temperature Cofired Ceramics (LTCC) are generally known. One such example is disclosed in U.S. Pat. No. 5,382,931, entitled xe2x80x9cWaveguide Filters Having A Layered Dielectric Structurexe2x80x9d which issued to A. J. Piloto et al. on Jan. 17, 1995. The Piloto et al. patent discloses the concept of waveguide filters having a dielectric structure for resonating at a predetermined frequency and having a series of longitudinally spaced resonators. A waveguide filter structure is disclosed where a predetermined number of contiguous layers of low temperature cofired ceramic (LTCC) are stacked, cofired and then plated with a conductive material. A series of vertically placed vias are positioned so as to form the perimeter of the filter.
The concept of evanescent mode waveguide bandpass filters including ridged waveguides with metal filled vias is also disclosed, for example, in the publication xe2x80x9cEmbedded Waveguide Filters For Microwave and Wireless Applications Using Co-fired Ceramic Technologiesxe2x80x9d, J. Gipprich et al., 1998 International Symposium on Microelectronics, pp. 1-4.
A publication entitled xe2x80x9cLow Temperature Co-fired Ceramic (LTCC) Ridge Waveguide Bandpass Filtersxe2x80x9d, Y. Rong et al., 1999 IEEE MTT-S Digest, pp. 1147-1150 further discloses a ridge waveguide filter including a transition from a ridge waveguide member to stripline.
Other examples are well documented in the literature and can be referred to for further details of such devices.
Accordingly, it is an object of the present invention to provide an improvement in waveguide filters.
It is a further object of the present invention to provide an improvement in ridge waveguide filters fabricated in a multi-layer dielectric medium.
It is yet another object of the present invention to provide an improvement in evanescent mode waveguide bandpass filters that are smaller in size, have lower insertion loss, exhibit wideband spurious suppression, and provide an easy transition to stripline transmission lines.
These and other objects are realized by a ridge waveguide filter which is formed of metallized blind vias in a plurality of contiguous layers of a dielectric medium including low temperature cofired ceramic (LTCC), high temperature cofired ceramic (HTCC) or organic printed wiring boards (PWB) in the fabrication of the waveguide sidewalls and solid ground planes to provide top and bottom walls as well as in the formation of a plurality of ridge waveguide sections in an embedded ridge waveguide structure. Patterns of conductive metal are selectively printed on the outer surface of certain dielectric layers to electrically short all the vias in the ridge waveguide sections and the adjacent wall vias so that the elements behave as though they comprise a solid metal structure.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific example, while disclosing the preferred embodiment of the invention, it is provided by way of illustration only due to the fact that various changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.